This invention, in one of its aspects, pertains to thrust chambers of liquid propellant rocket engines, and particularly to liquid bipropellant rocket engines. Bipropellants consist of fuel and oxidizer carried separately in the rocket and brought together in the engine. Thrust chambers for such engines include three principal components, the combustion chamber where rapid high-temperature combustion takes place; the converging-diverging nozzle where the hot reaction gases are accelerated to supersonic velocities; and an injector which contains a plurality of injection elements to meter the flow of propellants at a predetermined rate and fuel to oxidizer mixture ratio, introduce the mixture into the combustion chamber, and cause them to be atomized within the combustion chamber so that combustion takes place evenly.
In a particular aspect, the invention herein pertains to injectors. Through the years a number of injector types have evolved. Impinging spray injectors such as doublet and triplet impinging stream injectors, inject the fuel and oxidizer in intersecting sprays which break up and atomize the feed. The shower head injector sprays propellant into the combustion chamber through concentric rows of holes. There are also self impinging, and non-impinging stream patterns.
Evolving from the spray-type injectors are tube injectors. These tube injectors have injection elements for injecting the oxidizer into the combustion chamber as best understood from FIGS. 1 and 2 in the accompanying drawings. More specifically the invention herein pertains to tube injection elements. One tube injection element is the variable injection area type tube injection element shown in FIG. 1. This tube injection element consists of a tube 2, having a plate 4 covering its end opening into the combustion chamber 6, and a pintle 8 loosely holding the plate to provide for the variable input area. Fuel 10 is admitted through orifice 12 controlled by adjusting sleeve 14.
It will be appreciated that back pressure, although quite difficult to control in the variable area tube injection element 1 shown in FIG. 1, is an essential requirement. If the pressure drop is too low oscillatory combustion will result. In the case of the variable area injection element, either the maximum opening created by plate 4 will be too small and an excessive back pressure will develop, or the minimum opening will be too large and flow will be erratic and oscillatory. This design difficulty led to a tube injection element 20, shown in FIG. 2. This tube injection element has a secondary oxidizer chamber 21 to take care of back pressure. In addition tangential entry slots are provided to swirl the incoming oxidizer.
Referring to FIG. 2, from primary oxidizer chamber 22 oxidizer, by gas pressure or pumps is forced into tube injection element 20 and through tangential orifices (not visible) whose sizes are based on system pressure, and whose appearance is similar to orifices 24 opening into central injection element passageway 26 which is the inner of two concentric passageways. Flow is through an oxidizer manifold, and in response to a computer controlled oxidizer control valve, also not illustrated.
When the pressure increases due to increases in the required engine power level, back pressure is mitigated by shunting oxidizer from primary oxidizer chamber 22 to a secondary oxidizer chamber 21 whose orifices 24 are shown. From the secondary oxidizer chamber, the oxidizer, including that which is bled off, flows into tube injection element 20, being tangentially injected into the inner central passageway 26. There it joins flow from the primary oxidizer chamber 22, whose orifices cannot be seen but which are similar to those in the secondary oxidizer chamber 21.
Concomitantly, from a separate fuel chamber, rocket fuel flows into the outer channel 27 of the two concentric passageways, 26 and 27, also through orifices 25 adapted for tangential oxidizer entry. The spins imparted by the tangential oxidizer orifices cause the fuel and oxidizer streams to meet and mix as they are injected into the combustion chamber 29.
It is to be understood that as in the case of the variable input area injection element, the injection element having primary and secondary oxidizer chambers is also subject to improvement. Throttle range is limited to a maximum value in excess of 10:1. The injection element requires an external flow divider valve and actuator to control the flow split between the primary and secondary chambers. It also requires purges during start-up and shut-down to prevent backflow. The oxidizer and fuel must be metered at predetermined rates and mixture ratios in order to mix within the combustion chamber so that combustion takes place smoothly and completely. Control, thus, is quite demanding using either of the two prior art tube injection elements. By the practice of this invention the problems generated by both of the prior art tube injection elements are overcome. A tube injection element is provided herein which not only eliminates the need for a secondary oxidizer chamber, but permits the use of a smaller oxidizer flow control valve.